This invention relates to the formation of more efficient seals in the stuffing box assembly of pumps and valves, and like structures, through the use of a reformable packing ring comprising compressed particles of flexible graphite.
Flexible graphite has long been employed as a packing material to form very efficient seals for the stuffing box assembly of pumps, valves, and like structures. One form such flexible graphite has taken is that of preshaped lamellar rings. Another form is die molded rings formed by compressing a corrugated ribbon or tape of flexible graphite which has been wrapped about a shaft. In any event, in order for such preshaped rings to be effective, they must form an exact interference fit between the stuffing box and the stem of the pump or valve, or be capable of expanding and filling this space when pressure is applied by the tightening of the gland of the stuffing box. Unfortunately, however, lamellar packing rings, because of their highly anisotropic structure, do not undergo any significant amount of lateral flow when pressure is applied to them and hence often fail to form the desired interference fit between the stuffing box and stem of the pump or valve. Likewise, the die molded rings undergo an average expansion of only about 4 percent in their outer diameters before permanent impairment of the sealing surfaces of such rings occur, and also often fail to provide a satisfactory seal.